Beetle Pollination of Calycanthus floridus L.: Pollinator Behavior as a Function of the Volatile Flower Oils

McCormack, Jeffrey

ABSTRACT: The flowers of Calycanthus floridus L. are pollinated by beetles. At least 41 species of Coleoptera (representing 16 families) are involved, however only the Nitidulidae and Scolytidae are of major significance as pollinators. Pollinator behavior and movements are influenced to a large extent by floral odor, and by the development and movements of floral parts. The flower was found to be strongly protogynous, and seed development normally occurs only with the intervention of pollinating beetles. Pollination efficiency is related to the composition of the pollinator spectrum; the most significant factors being the density of the beetle vestiture and the behavior of beetles in the flowers. Many of the beetles found in the flowers have fungal associations at some stage in their life cycle. The floral essential oils of C. floridus were found to be a complex mixture with an approximate composition as follows: oxygenated sesquiterpenes, 47%; sesquiterpene hydrocarbons, 16%; monoterpene hydrocarbons, 11%; oxygenated monoterpenes, 15%; and straight chain alcohols and carbonyls, 11%. Beetles are significantly attracted to the odor of intact flowers and the total flower oil, but are not attracted to the odor of intact leaves or the total leaf oil. Some of the floral attractants were shown to be 1-terpinen-4-ol, ©<-terpineol, bornyl acetate, hexanol, and possibly cis-3-hexenol. Linalool acted as a repellant, but only when used in large amounts. Attraction of pollinators to C. floridus appears to be by production of imitative odors, that is, the floral odor may be chemically similar to the odors produced by certain fungi. A low molecular weight component of the flower oil had a mushroom-like odor which may have some significance in attraction, especially in view of the fungal associations of the majority of the pollinators.